The goal of this research is to continue studies concerned with the biochemical characterization of acid phosphatase 5 and its clinical implications in hairy cell leukemia, Gaucher's disease and bone malignancies. Much more in-depth understanding of tartrate-resistant acid phosphatase in pathological specimens has been achieved in recent studies. Our effort attempting to distinguish varieties of acid phosphatase and their clinical significance was reviewed at the Workshop sponsored by New York Academy of Science. An immunochemical approach has been used to compare different types of acid phosphatases. An antibody specific to prostatic acid phosphatase allows immunohistochemical identification of metastatic prostatic cancer. An enzyme immunoassay method was established in our laboratory. The new method provides much more accurate analyses of acid phosphatase band 5 in serum than the classic colorimetric method. Over 500 sera from cancer patients have been analyzed and the data are being evaluated concerning the value of acid phosphatase band 5 as an indicator of osteolytic activity.